Differential electromagnet having snap action



H. M. OGLE Feb. 17, 1948.

DIFFERENTIAL ELECTROMAGNET HAVING SNAP ACTION Filed Aug. 29, 1944 .l ...El

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Paiented Feb. 17, 1948 DIFFERENTIAL ELECTROMAGNET HAVING SNAP ACTION Hugh M. Ogle, Schenectady, N. Y., assignor to General Electric Company, a corporation oi' New York Application August 29, 1944, Serial No. 551,731

4 Claims. (Cl. 175335) My invention relates to differential control devices, more particularly to double coil electrornagnetic differential relays, and has for its object a simple and reliable device having snap operation from one position to another.

My invention has particular application to differential relays provided with two coils and with an armature pivotally movable from one psition to another in response to the differential energization ci the coils.

In carrying out my invention in one form, I provide a three-legged core with a coil mounted on each of the two outside legs and an armature extending across the three legs and spring I pressed against a dat face provided on the middle leg. Thus, when the coils are energized, the armature is held by magnetic attraction against the middle leg and upon a predetermined diiierential energization of the coils is moved with a snap action in each direction to an attracted position, and upon a decrease in the differential to a predetermined value the armature is moved to a neutral position or mid-position.

For a more complete understanding oi my invention, reference should be had to the accompanying drawing in which Fig. 1 is a, side elevation view partly in section of a differential relay embodying my invention; Fig. 2 is a sectional view taken along the line 2--2 of Fig. 1

ioollnng' in the direction of the arrows; Fig. 3 is a sectional view taken along the line 3--3 of Fig. i looking in the direction of the arrows;

iig. 4 is an enlarged simpliiied view showing features oi operation of the device; while Fig. 5 is a simplified wiring diagram showing typical electric connections for the two coils.

In carrying out my invention in one form, I provide a three-legged core l having coils 2 and mounted on the two outside legs t and 5. Extending across the three legs is a fiat bar shaped armature t having on its opposite ends movable electric switch 'contacts l and 8 which cooperate with stationary contacts 9 and i0.

For the purpose of giving the armature 8 a4 snap action in moving pivotally from the unat' tracted neutral position or mid-position shown in the drawing toward one or the other oi the outside core legs t and l5, I provide a dat bearing surface for the armature on the middle core threedegged core. The armature 6 has a middle portion provided with a :dat surface in engage- 2 ment with the lower fiat side or surface of the bar I2 and is biased by a spring stripji to that position, as seen in Fig. 1, the movable end of the spring strip lll, engaging the armature at the center of the armature.

As shown in Fig. 1. the armature as held by the spring I3 against the ilat lower side of the bar I2 is at each end in equally spaced relation with the ends of the core legs t and 5, this position of the amature being an intermediate unattracted position. During the operation of the device, it is contemplated that the coils 2 and 3 will both be energized and operation of the arma.- ture by magnetic attraction toward one or the other of the pole faces formed by the ends oi the legs 4 and 5 will be' obtained by increasing relatively the excitation of the coil toward which the amature is to be attracted.

When the two coils are energized, it will be observed that the middle portion of the armature is pulled by magnetic attraction against the at face of the bar l2, which magnetic force, in addition to the force applied by the spring i3, opposes pivotal movement of the armature toward either one of the core legs 4 and 5. This magnetic attractive force is effective in giving the armature a snap action. Thus, the net magnetic force applied to one end of the armature 8 is increased by increasing relatively the energization of the particular-coil 2 or 3 until finally the magnetic holding force of the middle leg and the force of the spring are overcome. However, when the armature 0 starts to move and is pulled away from the bar I2, the magnetic force between the bar and the armature decreases very rapidly while magnetic force applied to the end of the bar moving toward its attracted position increases rapidly thus providing a snap action in the movement of the armature.

As seen in Fig. 4, the armature has been moved counterclockwise by the coil 3 to an attracted position with respect to the core leg 5 with the Contact 8 in engagement with the contact i0. It will be observed that when the armature starts to move, it pivots about one or the other of the spaced-apart kniie-edge bearings formed by the lower edges of the bar i2. .fis shown, in moving counterclociiwise, the armature pivots on the right-hand lower edge i4.

Another feature of the device is that when the differential excitation is decreased to a predetermined value the armature is snapped by the spring back to the mid-position or unattraeted position shown in the drawing without snapping through the neutral position to the other atassume tracted position. Thus, a definite neutral position is provided bythe flat bar I2.

The magnetic attraction between the bar I2 and the armature is not indispensable to snap action. The coils may be connected so as to vgive little if any flux in the middle leg or the middle leg could be non-magnetic for some applications.

In ,Fig 5, I have shown simplified electric connections for the control of the coils 2 and 2. One terminal of each of the coils 2 and 2 is connected to the same side of a direct current supply source I2, while the other two terminals of the coils are connected to each other through a control resistance I6. The connection of the coils are such that the magnetic flux flows in the same direction in the two outer legs with respect to the middle leg, i. e. toward or away from the respective ends of the armature. A movable contact ann I'I cooperating with this resistance is connected to the other side of the supply source I5. This contact arm is suitably turned, as by ashaft I8 driven from a control device or instrument, whereby the relative energizations of the coils are changed. When the contact arm I1 is in its central position on the resistance I6, as shown in Fig. 5, the currents in the two coils are equal to each other and the armature then stands in its normal unattracted position, as shown in Fig. l. The relay may be used to control, for example, an electric motor or operating device to move an object in accordance with the movement applied to the shaft I8.

Referring to details of construction of the device, a base member I2 is provided made of electrically insulating material. such as a molded plastic material. The core I is secured to this base by means of two straps 2U and 2i secured by bolts on opposite sides of the middle core leg and having their lower ends bent outward and secured by the screws 22 land 23 to projections 2l and 25 on the upper surface of the support. I2. The bar I2 is positioned between the lower ends oi the straps 20 and 2I and the projection so as to be secured in place by the screws 22 and 22.

The stationary contacts 9 and III are mounted on spring strips 26 and 21 made oi' electrically conducting material, one end of each of the strips being secured by a suitable screw to a projection on the upper side oi' the support I2. With par ticular reference to the strip 26, a depression is provided in each of the two abutments or projec tions 28 and 29 for opposite ends of the strip, the upper end as viewed in Fig. 3 being secured by a screwl 20.

At its upper end the bar 2| is bent over laterally to form a support for an enclosing cover 2|. Also mounted on the support I9 are electric terminals 22 for the coil 2 and terminals 22 for the coil 2. Terminals are also provided on the heads of the screw 30 and the screw 24 securing the strip 21. Also, the head of the screw 22 is provided with a terminal whereby an electric connection can bel made with the armature 6 and the movable con tacts 'I and 8.

Another feature of my invention is that the differential current required for operation of the armature increases with the sum of the currents inthe coils. In other words, with high current values in the coils, a greater differential current is required for operation of the amature. This is' because the increased total current gives increased magnetic holding eiect between the bar I2 and the amature.

Referring to Fig. 3, a spring sheet member 3' is provided below the amature for securing the armature in the relative position shown in the drawing. This member 25 is stamped from a sheet oi thin spring material, such as phosphor bronze. It is provided with a central portion of substantially the same over-all outline as the bar I2 with an aperture at each end through which the clamping screws 22 and 22 extend. Metal spacer members 28 and 21 having the same thickness as the amature are provided between the member 25 and the bar l2. Also, in this central transverse portion an aperture 28 is provided through which extends the end of the spring l2 into engagement with the armature. The spring I2 is secured at its opposite end to the base member I9 as by suitable rivets.

The spring member 25 also has two portions 22 and 4I) extending lengthwise with respect to the armature and having their ends secured as by spot welded connections 4I and I2 to the armature. Thus, it will be observed that the spring member 25 secures the armature against movement in its own plane, although the member is made of thin flexible material and, therefore, does not offer any appreciable spring opposition to pivotal movement of the armature.

While I have shown a particular embodiment of my invention, it will be understood. of course, that I do not wish to be limited thereto since many modications may be made, and I, therefore, contemplate by the appended claims to cover any such modiilcations as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A diierential control device comprising a. magnet core provided with at least two legs, a coil on each of said core legs, a support between said core legs provided with spaced-apart knifeedge bearings, an armature extending across the ends of said core legs, a spring biasing said armature againstsaid bearings in an intermediate unattracted position with each end of said armature in spaced unattracted relation with the end of the adjacent core leg, and electric circuit connections for energizing said coils differentially thereby to produce snap pivotal movement of said armature on one or the other of said bearings toward one or the other of said core legs. upon predetermined diilerential energization of said coil. said spring being constructed and ar'- ranged to secure said armature in said interme. diate unattra'cted position when said dierential energization is reduced thereby to produce reverse snap movement of said armature away from one of said core legs.

2. A dierential control device comprising an E-shaped magnet core, a coil on each' of the two A outside legs of said core, spaced-apart knife-edge bearings on the end of the middle core leg. an armature extending across the ends of said core legs, a spring biasing said armature against said knife-edge bearings with each end of said armature in spaced unattracted relation with the end oi the adjacent outside core leg, electric circuit connections for energizing said coils substantially y equally whereby said armature is held magnetwhen said diierential energization is reduced to produce reverse snap movement of said armature away from one of said outside legs.

3. A differential control device comprising an E-shaped magnet core, a coil on each of the two outside legs of said core, said middle core leg being provided with a at surface on its end, an armature provided with a central fiat surface ex tending across said core legs, a spring biasing said armature against said middle core leg with said ilat surfaces in engagement with each other and with each end of said armature in spaced unattracted relation with the end of the adjacent outside core leg, electric circuit connections for energizing said coils substantially equally whereby said armature is held magnetically against the middle core leg, and means for varying the energization of said coil differentially thereby to -produce snap pivotal movement of said armature on one edge of said middle core leg toward one or the other of said outside core legs, said spring and the magnetic force of the middle core leg being arranged to secure said armature with said at surfaces in engagement with each other when said differential energization is reduced to produce reverse snap pivotal movement of said ar-A mature away from one of said outside core legs.

4. A diierential control device comprising an.

E-shaped magnet core, a coil on each of the two outside legs of said core, a bar on the end of the middle core leg provided with a fiat surface, an armature provided with a central flat surface extending across said core legs, a spring biasing said armature against said bar with said iiat surfaces in engagement with each other and with each end of said armature in spaced unattracted relation with the end of the adjacent outside core leg, electric circuit connections for energizing said coils substantially equally whereby said armature is held magnetically against said bar, and means for varying the energization of said coil differentially thereby to produce snap movement of said armature on one edge or the other of said bar toward one or the other of said outside core legs, said spring and the magnetic force of said middle core leg being arranged to secure said armature in an intermediate position against said bar when said differential energization is reduced a predetermined amount to produce snap movement away from one of said outside core legs.

HUGH M. OGLE.

REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 987,192 Turbayne Mar. 21, 19171 1,003,416 Barry Sept. 19, 1911 1,217,759 Hamilton Feb. 27, 1917 1,422,523 Beach July 11, 1922 2,240,677 Sonnemann et ai. May 6, 1941 2,307,077 Reagan Jan. 5, 1943 2,398,681 Weber Apr. 16, 1946 

